1. Field of the Invention
The present invention relates to a method for producing a double-sided pressure-sensitive adhesive sheet (PSA sheet) using an aqueous dispersion-type pressure-sensitive adhesive (PSA) composition with a nonwoven fabric as a substrate, and more specifically relates to a method for producing a double-sided PSA sheet whereby the inherent performance of the adhesive is more properly reflected in the produced PSA sheet.
This patent application claims priority from Japanese Patent Application Publication No. 2006-330516 filed on Dec. 7, 2006, the entire contents of which are incorporated herein by reference.
2. Description of the Related Art
Double-sided PSA sheets using a nonwoven fabric as a substrate (support) are widely used in household appliances, automobiles, office automation equipment and various other fields as a convenient and reliable means of joining. Examples of documents of prior art relating to such double-sided PSA sheets include Japanese patent Application Publication Nos. 2004-067875, 2002-356660, 2006-143856 and 2001-152111.
Because of the way they are used, double-sided PSA sheets must have the property of adapting to the surface shape (including irregularities and curves) of the adherend, a property that can be evaluated in terms of strong curve adhesiveness or low repulsion. If adaptability is lacking, the double-sided PSA sheet will be liable to joint floating, peeling and the like when used for attachment to parts with complex surface shapes, as in the case of automobile interiors and the like.
In the past, the PSA compositions used in producing double-sided PSA sheets have generally been solvent-type compositions of adhesive components (polymers and the like) dissolved in organic solvents. In recent years, however, due to environmental concerns and the desire to reduce the amount of volatile organic compounds (VOCs) released from double-sided PSA sheets, there has been a trend toward aqueous dispersion-type (aqueous) PSA compositions comprising adhesive components dispersed in water. Such conversion to aqueous PSA compositions has been studied in a variety of fields not limited to PSA compositions for double-sided PSA sheets, and current development is aimed at aqueous dispersion-type PSA compositions capable of providing adhesive properties (including the adaptability discussed above) equal to or greater than those of solvent-type PSA compositions.
However, compared to double-sided PSA sheets using solvent-type PSA compositions, in the case of a double-sided PSA sheet comprising a nonwoven fabric substrate with PSA layers formed using an aqueous dispersion-type (typically emulsion-type) PSA composition, the inherent performance of the PSA may not be properly reflected in the performance of the double-sided PSA sheet. Specifically, even if the aqueous dispersion-type PSA composition is capable of forming a PSA layer that exhibits good adaptability with respect to the surface shape of an adherend as evaluated from the properties of the PSA layer itself (that is, the PSA film without the nonwoven fabric substrate), adaptability may be much less when a double-sided PSA sheet is actually formed on a nonwoven fabric substrate using the composition. This has been one factor inhibiting conversion from solvent-type PSA compositions to aqueous dispersion-type PSA compositions in the field of double-sided PSA sheets.